<h3>描述</h3>
<p>通过beforeRemoveItems定义用户点击删除按钮，文件删除前事件</p>
<h3>示例</h3>
<p>点击删除按钮，延时1秒后文件删除</p>
<ti-upload [url]="url" (beforeRemoveItems)="onBeforeRemoveItems($event)"></ti-upload>
